Micro-photonics parallel data transmission fabric and interconnect

Descriptions are generally related to optical communication, and more particular descriptions are related to optical communication with micro-photonics devices.

Computer systems in server environments have frequent need to transfer large amounts of data between components separated by distances measured in the range of centimeters, as well as between components separated by distances much farther than short-centimeter lengths, even into the range of meters.

Currently, laser-based photonics are the leading candidate technologies for communication of the longer distances, such as communication from rack to rack in data centers or from chip to chip. Traditionally, a discrete laser pumps light into a silicon photonics chip that takes electrical signals from one device and produces light signals to transmit to other devices via optical fibers. Such an approach involves circuit complexity, increases cost for components, and has high power requirements, which results in requirements for cooling.

Traditionally, addressing the need for increased I/O (input/output) bandwidth involves driving electrical signals at higher speeds with more complex encoding methods. Increasing I/O to higher speeds and more complex encoding increases the need for BER (bit error rate) correction mechanisms to ensure proper communication between components. Modern application of electrical I/O (EIO) use a large serializer/deserializer (SerDes or SERDES). Increasing EIO data rates causes the SerDes to become a bottleneck, which increases latency of the communication.

Additionally, power efficiency in the SerDes path does not scale well with increasing EIO data rates, resulting in system power consumption that exceeds system specifications. Traditional laser-based silicon photonics optical I/O (OIO) typically uses materials (such as III-V semiconductor components) that increase component costs. Traditional laser communication also has high power requirements, requiring cooling, and increasing power consumption to levels that exceed system specifications.

Descriptions of certain details and implementations follow, including non-limiting descriptions of the figures, which may depict some or all examples, and well as other potential implementations.

As described herein, a system enables optical communication with direct conversion of the electrical signal into an optical signal with an array of micro-scale optical sources. The use of the array of optical sources can eliminate the need for a large serializer/deserializer (SerDes or SERDES). With an array of optical sources, the optical communication can occur at lower power and lower frequency per optical source, with multiple parallel optical sources combining to provide a signal.

Reference to micro-scale optical devices can refer to optical transmitters, optical receivers, or optical transceivers integrated into or onto a semiconductor substrate. Each of the optical devices can have a footprint on the substrate of approximately less than 100 square microns (100 μm). Thus, a micro-scale device as described herein can have a size on the order of single-digit microns per side for approximately square shapes, or in diameter for approximately round devices (e.g., device having dimensions of approximately 5 μm by 5 μm up to approximately 10 μm by 10 μm). In one example, each transmitter and each receiver has a footprint of less than 10 μm, with dimensions of approximately 1 μm by 1 μm to approximately 3 μm by 3 μm.

Reference to micro-scale optical devices can indicate optical devices that have dimensions in the micro (i.e., 10meter) scale or smaller. Thus, the systems and configurations described can be implemented with optical devices in the micro-scale or with optical devices having dimensions in the nano (i.e., 10m) scale. For simplicity in description throughout, reference is made to micro-optics or micro-scale devices, which will be understood to refer to devices having dimensions in the low (e.g., single digit) microns, or devices in having dimensions in the scale of nanometers.

A system with an array of micro-scale optical devices can replace traditional electrical input/output (EIO) transmission paths that run through a high-power SerDes to waveguides with a native on-die fabric conversion to optical input/output (OIO). The waveguides can be electrical or optical waveguides. The native conversion of electrical signals to OIO with an integrated array of micro-scale optical devices, such as a micro light emitting diode (μLED) array or array of vertical cavity surface emitting lasers (VCSELs).

Native conversion of electrical signals to OIO can improve power and performance requirements for input/output (I/O) in compute platforms with on-die fabrics. The use of micro-scale optical devices can be compatible with multiple different types of encoding, which allows for scalable data transmission rates. In one example, in place of a high-bandwidth signal from a laser source that transmits many sequential bits at high frequency, micro-scale optical transmitters and receivers can split a signal into multiple parallel parts and send a slower signal over many parallel links. The signal can be split at the transmitter end with the control circuitry into multiple parallel portions, and combined at the receiver end by optical receiver control circuitry.

It will be understood that laser light has greater range or reach in terms of the distance a signal can travel and still maintain a bit error rate within expected tolerances as compared to LED light. Thus, replacing a high-power light source with a lower-power light source will tend to result in an optical signal with a shorter reach. In one example, the system can include optical signal repeaters, similar to electrical re-timers, which can convert the optical signals into electrical signals and then regenerate the optical signals in the waveguides.

The system can include a plurality of waveguide bundles (such as a bundle of fiber cores) to transmit the optical signals from the array of optical sources. In one example, the system enables many-waveguide bundles to be manufactured without concern for relative rotation of fibers within the bundle, as long as the connectivity at each end is common. In one example, the system can apply alignment training operations to reduce the requirement for exact fiber placement within the connectors.

With the use of micro-optical device arrays integrated into a system chip, low energy, inexpensive optical technologies traditionally applied to consumer electronic devices can provide an optical communication system with many power-efficient devices in parallel. The consumer electronic devices can include television and computer displays, smart watches, AR/VR (augmented reality/virtual reality) displays, laptops, tablets, mobile phones, and so forth.

A communication system based on micro-scale optical devices can provide optical communication signals to a plurality of waveguides. The micro-scale optical device can convert EIO to OIO with data encodings that can sustain high bandwidth communication. The system can apply optical repeaters to extend the reach of LED devices. The system can enable self-training to provide resiliency and cable manufacturing corrections, reducing the need for precision manufacturing control over the alignment of the waveguides, which can have potentially dozens of waveguide cores having small diameter to transmit the optical signals.

is a block diagram of an example of a communication system based on an array of micro-scale light sources. Systemrepresents a communication system based on a data network with micro-optical devices. Electrical signalrepresents a signal to be transmitted from one component to another component.

TX (transmit) circuitrepresents an electrical transmission circuit that generates signal, which represents one or more control signals that trigger micro-optics to generate electrical signalinto an optical signal. μLED arrayrepresents an array of micro-optic devices. The devices in the array are lower power than traditional laser communication devices, and can be integrated directly into a substrate without III-V materials.

μLED arraygenerates OIO to transmit over MCF (multicore fiber). Signalrepresents a parallel optical signal or OIO transmitted over MCFby μLED. In one example, systemincludes repeaterto repeat the OIO to extend the distance the optical signals can travel.

If systemincludes repeater, systemincludes MCF, which represents an optical second multicore waveguide to transmit repeated optical signalto the target. If systemdoes not include repeater, MCFcan provide optical signaldirectly to the target device.

PD (photodetector) arrayrepresents an optical detector or photodiode in the receiving device. Signalrepresents an electrical signal based on the conversion of optical signal(or optical signal) into an electrical representation of the communication by PD array. RX circuitrepresents a receive circuit in the electrical domain to transmit electrical signalto a processor for processing at the receiving device. In contrast to a traditional optical communication system, systemincludes μLED array, and corresponding PD array. PD arraycan also be considered an array of micro-optical devices.

The arrays of micro-optical devices are intrinsically small, energy-efficient devices, which can provide high signal density in network fabrics between silicon dies. In one example, each data wire in the TX and in the RX direction is paired to one or more μLEDs for optical transmission or receiving detection, and paired to a circuit to amplify received photons. The pairing can represent a “pixel” in the transmit stage and receive stage, regardless of how many μLED devices in the array are used in the composition of the frequencies (colors) in the pixel. Systemcan represent an overall link assembly as a data channel between a first electronic device (a transmitter) and a second electronic device (a receiver). The transmitter and receiver for one transmission can swap roles for a subsequent transmission.

The use of μLED arrayor other micro-scale optical devices in systemcan enable a system with optical sources and optical receivers integrated directly into a system substrate without requiring special materials and special semiconductor processing needed for laser devices. The micro-optics can be driven directly by control circuitry, resulting in much faster processing of communication signals while using significantly less energy. It is estimated that micro-optics based communication can improve the speed and energy per bit by approximately 10-100× over traditional laser photonics.

In one example, systemcan include μLED arraywith μLED components measured on the order of 1 μm (micron) in size. In one example, systemcan include μLED arraywith μLED components that operate at data rates on the order of 1 GHz per μLED. Combining the small size and the data rate, systemcan achieve a level of bandwidth from a piece of silicon that exceeds other approaches that rely on 2.5D or 3D interconnects for any kind of I/O technology. In contrast to laser photonics, in one example, systemcan apply μLED technology that can run at extended temperature ranges, bypassing many of the precision cooling challenges and costs associated with standard laser-based photonics while consuming less energy per transmitted bit, on the order of 10× less energy. Such improvements are possible without the constant overhead power draw of a laser. The overall μLED technology can be implemented at a component-level cost that is much lower than more complex electrical connectors and cables, or laser-based photonic components (e.g., laser, connectors, cables).

is a block diagram of an example of a communication system with a connector to transmit light from a micro-scale light source. Systemrepresents an example of a communication system in accordance with an example of system.

The computational demands of compute devices, such as CPUs (central processing units), GPUs (graphics processing units), FPGAs (field programmable gate arrays), XPUs (accelerator processing units) or other accelerator devices, and interconnects, continues to show exponential growth. The demand for data throughput also rises exponentially to support the exponential growth of computational demand.

At the package level, such demand causes corresponding growth in pin count, which is heavily driven by memory requirements, such as volatile memory (e.g., DRAM (dynamic random access memory)) and nonvolatile memory (NVM). The demand for data throughput increases the demand for I/O, which means the overall package power to deliver a target I/O rate would continue expanding exponentially.

High-speed SerDes in electrical wires and silicon photonics are the leading candidates to continue the increase in I/O throughput. However, increasing to higher data rates tends to result in higher bit error rate (BER), leading to the implementation of mechanisms such as FEC (forward error correction) to control BER. BER control mechanisms tend to increase latency, which can work against the mechanisms employed to increase the data transmission rate. As area and energy increase due to the physical signaling requirements, complexity of the surrounding components (e.g., packages, boards, cooling) also increase, increasing system complexity.

In contrast to the traditional approaches, systemcan reuse the native compute fabric of the on-die design of a system with a micro-optics array. Such an array can provide a “wide” interface (e.g., on the order of 100 bits wide per direction) that can achieve high throughput even at lower operating frequencies than used by current systems (e.g., at speeds on the order of 1 GT/s (giga-transfer per second) per wire as opposed to 10 GT/s). Current implementations of μLEDs can be less than 7 μm×7 μm in size, with power consumption on the order of 0.03 pJ/b (picojoules per bit), and with the ability to operate at 0.5-10 GT/s depending on device design. Even factoring in wiring and receiver gain from photodetectors, operation of μLED based communications is expected to be less than 0.5 pJ/b for current implementations. Future generations of μLED devices are expected to be on the order of 1 μm, with power requirements of approximately 0.1 pJ/b. The reach of μLEDs is expected to be significantly larger (O(1)m) than electrical signals such as PCIe(peripheral component interconnect express), CXL (compute express link), UPI (ultra path interconnect), DRAM (dynamic random access memory), or others (O(0.1)m), but much less than laser-based silicon photonics (O(100)m) or VCSEL (vertical cavity surface emitting laser) (O(10)m).

Systemincludes photonics arrayfor communication. In one example, photonics arrayincludes an array of μLEDs and an array of micro-scale photodetectors (PDs) that can detect LED light. In one example, photonics arrayincludes an array of VCSELs and an array of micro-scale PDs that can detect the VCSEL light. For simplicity, photonics arraywill be referred to as array, which can include optical source devices and optical detection devices. In one example, arraycan be referred to as a dense array, referring to having a large number (e.g., on the order of 100 or 1000) of optical devices. Such an array is dense in that it has the large number of optical devices integrated in the same substrate as an array of devices.

Signal source/targetrepresents a component that can generate an electrical signal to transmit through array. Signal source/targetrepresents a component that can receive an electrical signal from arrayin response to detection of a signal from an external source. Signal source/targetcan be, for example, a system on a chip (SOC) component or a CPU or other component on the SOC, an FPGA, a GPU, an accelerator, or other component.

Controllerrepresents control circuitry that can trigger the transmit operation of array. For transmission, signal source/targetrepresents a signal source to provide an electrical signal to array. In response to the signal and control signals from controller, arrayconverts the EIO to OIO with micro-optical transmitters. In one example, the transmitters send the optical signal through lensto waveguides in connector. In one example, lensis an optional component. Connectorcan then transmit the optical signal to a target of the optical communication.

For receive, signal source/targetrepresents a signal target. Connectorcan receive an optical signal from an external component and provide the optical signal through lensto array. In one example, lensis an optional component. Optical detection components of arraycan detect the signal and convert the OIO to EIO to provide to signal source/target.

In one example, systemincludes lens actuator, which represents one or more components to steer lensto direct the optical communication signal. In one example, lens actuatorincludes one or more mechanical components. In one example, lens actuatorincludes one or more electrical components. Controllercan control the operation of lens actuatorto focus a received optical signal on the light detection components of array, or focus a transmit optical signal to waveguides of connector.

Arraycan be an array of micro-scale optical device integrated into a system substrate, such as a silicon chip of a communication fabric. Controllercan drive the components of arraywith electrical communication signals for transmit, and can control the components of arraywith control signals for receive.

is a block diagram of an example of a micro-LED circuit. SOCrepresents an example of a semiconductor chip with a micro-optical array in accordance with an example of array.

SOCincludes EIC (electrical integrated circuit) circuitsand μLED array. μLED arrayrepresents an array of micro-optical devices. μLED arrayspecifically illustrates transmit (TX) and receive (RX) devices. The arrangement of transmit and receive devices is not limiting, and any arrangement of transmitters and receivers can be used. EICcircuits represent electrical circuits to control the operation of μLED array. In one example, the elements or individual devices of μLED arrayrepresent devices of solid state materials, different from traditional organic LEDs. μLEDs can support very fast modulation by EIC circuits.

The components of μLED arraycan be highly parallel, allowing smaller portions of an overall optical communication to be transmitted/received on individual optical paths. Such an array of wide optical paths can allow transmission at lower speeds, which can result in a wider interface that provides the high bandwidth, even at lower operating speeds, referring to multiple optical links operating at a slower speed relative to one optical link that would need to operate at a higher speed to achieve the same bandwidth. The optical devices of μLED arraycan be driven directly by EIC circuitswithout requiring a large, fast SerDes. In one example, EIC circuitscan include parallel SerDes paths for the array of devices of μLED array. Such SerDes paths could be simpler and more efficient than one large device trying to feed a high-speed laser optical link. In one example, SOCincludes simple, standard optical encoders in EIC circuitsinstead of a large SerDes.

As mentioned above, micro-optical devices can be very small, with devices estimated to reach sizes as small as on the order of 1 μm. The individual devices of μLED arraycan be of a size of approximately 50 μm, or 25 μm, or as low as 10 μmor smaller. The devices of μLED arraycan directly convert electrical signals to optical to drive the signal on a waveguide, drive onto a fiber core, or through a waveguide onto a fiber core.

The individual components of μLED arraycan provide optical transmission as an array of μLED pixels for transmission, with a corresponding optical receiver on the target device. A pixel is composed of a number of μLEDs emitting distinct colors or light wavelengths, enabling μLED arrayto provide multilevel optical signals. A multilevel optical signal here refers to a signal with different wavelengths or colors, rather than an optical signal having different signal amplitudes.

In one example, μLED arrayis designed and laid out in an arbitrary pattern. The pattern can be structured into a collection of transmit and receive sites per channel of I/O transmission required. In one example, μLED arrayhas an arrangement of individual components or groups or collections of components to have multiple μLEDs transmit the same optical signal together as a single pixel.

Different groups of multiple μLEDs can transmit different color signals, for example, with one group of μLEDs as one pixel transmitting one wavelength optical signal, another group of μLEDs as a second pixel transmitting a second wavelength optical signal, and so forth. The color mixing by μLED arraycan produce a light pulse with specific standard color coordinates that can be deciphered at the photodetector side of the link. In one example, the maximum count of elements of the μLED array in a pixel is determined by the diameter of the individual fiber cores in the waveguide media, as well as the manufacturing tolerance for aligning waveguides to emitter/detector arrays.

In one example, each μLED-based pixel is transmitted down one waveguide fiber. In one example, multiple pixels are encompassed with multicore fiber material. In contrast to laser-based and VCSEL-based photonics, μLEDs can operate with very inexpensive plastic waveguide material that is commonly used in medical and science programs, such as light sources in dental offices, or cameras for interior inspection of living organisms, or factory lines. μLED technology is also capable of operating at extended temperature ranges and does not require complicated cooling solutions typical for standard silicon photonics and their associated laser modules.

In one example, μLED arrayrepresented μLED devices integrated into a silicon substrate of SOC. In one example, μLED arraycan provide a signal density of approximately 1 TB/s/mm(terabyte per second per square millimeter) off the silicon substrate.

In one example, μLED arrayhas roughly 2K (e.g., 2048) sites for transmission and reception of data. As described in more detail below, in one example, the micro-optical components can include components having transmit and receive capability, with the optical device structure capable of being a transmission/emitter device, or a receiver/detector of photonic energy. The mapping of individual TX/RX sites to I/O channels at the electrical level (e.g., ×16 lanes, ×8 lanes, ×11 lanes) can be any configuration, as long as the physical connector to move the optical signals from the μLED photonics to the other end for detection reflects the physical mapping applied.

In one example, the individual components of μLED arraycan be other optical or light sources, such as μVCSELs emitting light in visible-infrared range. In a specific example, the array of micro-optical devices can be an array of μVCSELs emitting light with wavelengths of 620 nm, 625 nm, 630 nm, and 635 nm in a 4 color μVCSEL array.

In one example, μLED arrayneeds support mechanisms for operation. A specific example can include the use of a voltage shifter or charge capacitor to increase voltage to reach the diode activation level (e.g., increasing from 0.7 V to 3 V). On the detector side, traditional photodetector circuits generate current in the nA (nano-Ampere) range, which can benefit from detection and amplification circuits with noise isolation.

In one example, the μLED array or other micro-optical device array is stacked on top of an underlying CMOS (complementary metal-oxide-semiconductor) circuit. The following illustrates different examples of μLED circuits combined with CMOS circuits.

is a block diagram of an example of a μLED circuit with a vertical connector interface for a communication system. Circuitincludes μLED, which represents a substrate with a μLED array, and circuitry, which represents electronic circuits that provide electrical signals to μLEDfor transmission and receive electrical signals from micro-receivers.

In one example, μLEDis bonded to circuitryby TGV (through glass via) attachment and connection to combine a μLED die or wafer to a CMOS die or wafer. The layers can thus be fused during the manufacture and assembly process.

Connectorrepresents a connector interface to the μLED circuits of μLED. Connectorcan be or include waveguides or lenses to enable a connector to connect vertically to the circuit.